linux-kernel - Re: [PATCH 4/5] usb: dwc3: Allow end transfer commands to be sent during soft disconnect

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Date:   Thu, 14 Jul 2022 00:19:04 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <quic_wcheng@...cinc.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH 4/5] usb: dwc3: Allow end transfer commands to be sent
 during soft disconnect

On 7/13/2022, Wesley Cheng wrote:
> Hi Thinh,
>
> On 7/12/2022 6:42 PM, Thinh Nguyen wrote:
>> On 7/12/2022, Wesley Cheng wrote:
>>> Hi Thinh,
>>>
>>> On 7/8/2022 6:58 PM, Thinh Nguyen wrote:
>>>> On 7/8/2022, Wesley Cheng wrote:
>>>>> If soft disconnect is in progress, allow the endxfer command to be
>>>>> sent,
>>>>> without this, there is an issue where the stop active transfer call
>>>>> (during pullup disable) wouldn't actually issue the endxfer command,
>>>>> while clearing the DEP flag.
>>>>>
>>>>> In addition, if the DWC3_EP_DELAY_STOP flag was set before soft
>>>>> disconnect
>>>>> started (i.e. from the dequeue path), ensure that when the EP0
>>>>> transaction
>>>>> completes during soft disconnect, to issue the endxfer with the force
>>>>> parameter set, as it does not expect a command complete event.
>>>>>
>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>>>>> ---
>>>>>     drivers/usb/dwc3/ep0.c    | 3 +--
>>>>>     drivers/usb/dwc3/gadget.c | 5 ++++-
>>>>>     2 files changed, 5 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
>>>>> index 506ef717fdc0..5851b0e9db0a 100644
>>>>> --- a/drivers/usb/dwc3/ep0.c
>>>>> +++ b/drivers/usb/dwc3/ep0.c
>>>>> @@ -290,8 +290,7 @@ void dwc3_ep0_out_start(struct dwc3 *dwc)
>>>>>             if (!(dwc3_ep->flags & DWC3_EP_DELAY_STOP))
>>>>>                 continue;
>>>>>     -        dwc3_ep->flags &= ~DWC3_EP_DELAY_STOP;
>>>>> -        dwc3_stop_active_transfer(dwc3_ep, true, true);
>>>>> +        dwc3_stop_active_transfer(dwc3_ep, true, dwc->connected);
>>>>>         }
>>>>>     }
>>>>>     diff --git a/drivers/usb/dwc3/gadget.c 
>>>>> b/drivers/usb/dwc3/gadget.c
>>>>> index bd40608b19df..fba2797ad9ae 100644
>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>> @@ -3696,8 +3696,10 @@ void dwc3_stop_active_transfer(struct dwc3_ep
>>>>> *dep, bool force,
>>>>>         if (dep->number <= 1 && dwc->ep0state != EP0_DATA_PHASE)
>>>>>             return;
>>>>>     +    if (interrupt && (dep->flags & DWC3_EP_DELAY_STOP))
>>>>> +        return;
>>>>> +
>>>>>         if (!(dep->flags & DWC3_EP_TRANSFER_STARTED) ||
>>>>> -        (dep->flags & DWC3_EP_DELAY_STOP) ||
>>>>>             (dep->flags & DWC3_EP_END_TRANSFER_PENDING))
>>>>>             return;
>>>>>     @@ -3744,6 +3746,7 @@ void dwc3_stop_active_transfer(struct
>>>>> dwc3_ep *dep, bool force,
>>>>>         __dwc3_stop_active_transfer(dep, force, interrupt);
>>>>>         spin_lock(&dwc->lock);
>>>>>     +    dep->flags &= ~DWC3_EP_DELAY_STOP;
>>>>
>>>> Can we clear this flag in __dwc3_stop_active_transfer(). It should 
>>>> apply
>>>> if End Transfer command was sent.
>>>
>>> I wanted to make sure that we weren't modifying the DEP flags outside
>>> of a spin lock.  Patch#3 modifies it where we unlock before calling
>>> __dwc3_stop_active_transfer(), so we can allow the dwc3 threaded IRQ
>>> handle events while the cmd status polling happens.
>>>
>>> Maybe we can unlock/lock the dwc3->lock inside
>>> __dwc3_stop_active_transfer() and that way we can ensure DEP flags are
>>> modified properly?
>>
>> I didn't realize that you unlock/lock when calling
>> __dwc3_stop_active_transfer(). We'd need to be careful if we want to
>> unlock/lock it, and avoid it all together if possible. It can be easily
>> overlooked just like dwc3_gadget_giveback().
>>
>> What issue did you see without doing this?
>
> I saw endxfer timeout issues if I didn't do it.  If we keep the lock 
> held, then the DWC3 event processing would be blocked across the 
> entire time we are waiting for the command act to clear.  With 
> unlocking before polling, then at least we're still able to handle the 
> EP0 events that are pending.
>
> It was definitely one of the harder scenarios to reproduce.  The main 
> patch series which resolved a lot of the issues early on was patch#1. 
> After adding that the other issues are seen maybe after a day or so of 
> testing.
>

I see. The soft-disconnect still go through right?
Can you try this and see if this works for you?

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 13e4f1a03417..4f67a484c490 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -451,7 +451,9 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, 
unsigned int cmd,

         dwc3_writel(dep->regs, DWC3_DEPCMD, cmd);

-       if (!(cmd & DWC3_DEPCMD_CMDACT)) {
+       if (!(cmd & DWC3_DEPCMD_CMDACT) ||
+           (DWC3_DEPCMD_CMD(cmd) == DWC3_DEPCMD_ENDTRANSFER &&
+            !(cmd & DWC3_DEPCMD_CMDIOC))) {
                 ret = 0;
                 goto skip_status;
         }


We can set it and forget it when we're about to de-initialize the 
controller. Just like what we've already done by not waiting for the End 
Transfer endpoint command completion interrupt.

Thanks,
Thinh